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Re: [Phys-l] explanatory and response variables (was calibration )



John's comments about independent and dependent variables reminded me of some questions I would like to pose to the group.

(1) What should we call the axes of a 2-dimensional graph (in general)?

horizontal and vertical
x and y
independent and dependent

I am amazed how many students don't know horizontal and vertical, but probably they are more familiar with that than with independent and dependent.

x and y are usually understood, and that is usually what spreadsheets call them, but it seems odd to call them x and y when we are not plotting y as a function of x, but perhaps plotting current as a function of voltage.

If we are plotting current as a function of voltage, is it just best to get over my hangup and tell the students that voltage is on the x-axis and current is on the y-axis?

(2) If I tell students to "plot current versus voltage," or my preferred way is to say "plot current as a function of voltage," many will ask which do I mean is the x-axis, etc. Those who don't ask seem to have a 50/50 chance of doing it backwards.

Am I old fashioned? If I use the phrase "plot current as a function of voltage" would most (all?) practicing physicists understand I am askling for current on y and voltage on x? If so, why aren't students learning this? If not, what terminology should I be using if I want to use what's being practiced?

(3) What alternative words do we have for a 3-D coordinate system? For a standard right-hand system I generally say the x-axis runs left to right (right positive), the y-axis runs backward to forward (forward positive), and the z-axis runs bottom to top (top positive).

I know axes can point anyway you want them to point, but do most people generally visualize it as I said? In textbooks we often see x to the right, y pointing up, and z pointing backwards. To me, that does not fit with other practical things such as numerically-controlled milling machines, etc.

Bottom line... if there is some standard language that is different than what I visualize, I have missed it, and so have many years of students. If there isn't any standard language, or if the standard is not being taught, no wonder students are confused.


Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton University
1 University Drive
Bluffton, OH 45817
419.358.3270
edmiston@bluffton.edu